Bottom Line:
This functional KO-phenotype was accompanied by cell-specific up-regulation of NCS-1 and Cav3.1-TTCC mRNA.Furthermore, in wildtype we identified an age-dependent switch of TTCC-function from contributing to SN DA pacemaker-precision in juveniles to pacemaker-frequency in adults.This novel interplay of Cav1.3 L-type and Cav3.1 T-type channels, and their modulation of SN DA activity-pattern and D2-AR-sensitisation, provide new insights into flexible age- and calcium-dependent activity-control of SN DA neurons and its pharmacological modulation.

Mentions:
To further define a functional compensatory phenotype in juvenile Cav1.3 KO mice, we next studied whether the mechanism of SN DA D2-AR desensitisation downstream of Cav1.3 was similar in the Cav1.3 KO to the Ca2+ sensor NCS-1 mechanism that we identified for WT mice11. To determine if D2-AR desensitisation in SN DA neurons from juvenile Cav1.3 KO mice depended on free intracellular Ca2+ and interaction of NCS-1 with D2-ARs, we buffered internal Ca2+ with 10 mM EGTA (whole-cell; Fig. 3a,d and Table 1), and in a second experiment we applied a membrane permeable peptide that prevents D2-R/NCS-1 interactions (perforated patch; DNIP, or scrambled DNIP (srDNIP) as control1126; Fig. 3b,d and Table 1). Internal Ca2+ buffering induced prominently desensitising D2-AR responses in SN DA neurons from both, juvenile WT and Cav1.3 KO mice (Fig. 3b,d and Table 1). Furthermore, the presence of the DNIP peptide (but not srDNIP) re-stored WT-like desensitising D2-AR responses in SN DA neurons from juvenile Cav1.3 KO mice (Fig. 3b,d and Table 1). These findings strongly suggest that the D2-AR desensitisation mechanism downstream of the Ca2+ source is not altered in SN DA neurons from Cav1.3 KO mice and relies — as in WT — on Ca2+-dependent NCS-1/D2-AR interactions11. These findings also indicate an alternative, compensatory Ca2+ source in SN DA neurons from Cav1.3 KO mice, mediating NCS-1/D2-AR interactions and the observed reduction in D2-AR desensitisation.

Bottom Line:
This functional KO-phenotype was accompanied by cell-specific up-regulation of NCS-1 and Cav3.1-TTCC mRNA.Furthermore, in wildtype we identified an age-dependent switch of TTCC-function from contributing to SN DA pacemaker-precision in juveniles to pacemaker-frequency in adults.This novel interplay of Cav1.3 L-type and Cav3.1 T-type channels, and their modulation of SN DA activity-pattern and D2-AR-sensitisation, provide new insights into flexible age- and calcium-dependent activity-control of SN DA neurons and its pharmacological modulation.